In recent years, a so-called inkjet method using an inkjet head has been widely employed in printing using ink on a print medium such as paper, in forming an orientation film or applying UV ink onto a substrate (transparent substrate) of a liquid crystal display device or the like, or in applying a color filter onto a substrate of an organic EL display device.
An inkjet printer (hereinafter including an oriented film forming device and a coating device) employing the inkjet method is provided with a liquid feeding device for feeding a liquid material from an ink tank to inkjet heads (specifically, liquid pool provided in each of inkjet heads). In this case, a large inkjet printer generally includes a plurality of inkjet heads. Accordingly, it is necessary to provide a plurality of liquid feed pipe lines for feeding the liquid material to the plurality of inkjet heads from the ink tank.
The liquid feeding device for inkjet heads of this type has a structure, for example, as illustrated in FIG. 12, in which inkjet heads 52 are each connected to a downstream end of each of a plurality of liquid feed pipe lines 51, which directly communicate with an ink tank 50, and a liquid feed pump 53 for pressure-feeding the liquid material from the ink tank 50 to each of the inkjet heads 52 is provided halfway on each of the liquid feed pipe lines 51. With this structure, the necessary number of liquid feed pipe lines 51, each of which directly communicates with the ink tank 50 and with each of the inkjet heads 52, corresponds to the number of the inkjet heads 52 to be provided, and the necessary number of the liquid feed pumps 53 also corresponds to the number of the inkjet heads 52 to be provided. As a result, the liquid feeding device is increased in size, a structure thereof is complicated, and costs thereof are increased.
As another example, as illustrated in FIG. 13, there is generally known a liquid feeding device having a structure in which inkjet heads 62 are each connected to a downstream end of each of a plurality of liquid feed pipe lines 61, which directly communicate with an ink tank 60, and a pressure source 63 for pressurizing the interior of the ink tank 60 is provided in place of the liquid feed pump. Also with this structure, the necessary number of the liquid feed pipe lines 61, each of which directly communicates with the ink tank 60 and with each of the inkjet heads 62, corresponds to the number of the inkjet heads 62 to be provided, with the result that the size of the liquid feeding device is increased and the costs thereof are increased. In addition, the liquid material is fed with a uniform pressure with respect to each of the inkjet heads 62, so it is necessary to set lengths of the plurality of liquid feed pipe lines 61 to be equal to each other, which also increases the size of the liquid feeding device and raises the costs.
As an example of a liquid feeding device which is devised so as to avoid those fundamental problems, Patent Documents 1 and 2 below disclose a structure in which a main pipe line which communicates with an ink tank, and a plurality of branch pipe lines, each of which is branched from the main pipe line, are provided, and inkjet heads are each connected to the downstream end of each of the branch pipe lines. Specifically, Patent Document 1 discloses a structure in which a pipe line communicating with a main tank is branched into a plurality of pipe lines, and the inkjet heads are connected to each of the branch pipe lines through a sub tank. Further, Patent Document 2 discloses a structure in which the main pipe line communicating with a solution tank is branched into a plurality of pipe lines, and the adjacent inkjet heads each connected to the downstream end of each of the branch pipe lines are brought into close contact with each other.
Further, as described above, the inkjet head of this type is provided with a liquid feed path for feeding the liquid material from the ink tank to the inkjet head (specifically, liquid pool provided in the inkjet head). In this case, when an amount of a dissolved gas contained in the liquid material to be fed to the inkjet head through the liquid feed path is equal to or larger than an allowable value (for example, 4 ml/1000 ml), air bubbles are generated in the liquid pool of the inkjet head. For this reason, when the liquid material is ejected from the liquid pool through the ejection nozzle, the appropriate ejection of the liquid material is inhibited while the air bubbles act as cushions.
Halfway on the liquid feed path of the inkjet head, there is provided a deaerating unit for reducing the amount of the dissolved gas contained in the liquid material to be smaller than the allowable value. In this case, for the conventional deaerating unit, there is used a hollow fiber membrane obtained by collecting into a bundle a plurality of hollow fibers, each of which is made of a gas-permeable film such as polytetrafluoroethylene (for example, see Patent Documents 3 to 5 below).
Specifically, the deaerating unit has a structure in which the above-mentioned hollow fibers are provided halfway on the liquid feed pipe for feeding the liquid material from the ink tank to the inkjet head, an outer peripheral side of the hollow fiber membrane is covered with a container which is an enclosure, and the interior of the container is depressurized to obtain a vacuum state, thereby removing the dissolved gas or the air bubbles from the liquid material passing through the hollow fiber membrane to deaerate the liquid material.
In this case, each unit hollow fiber of the hollow fiber membrane has generally an inner diameter of about 20 to 30 μm (in Patent Document 4, inner diameter of 50 to 500 μm). The diameter of the entire hollow fiber membrane is much larger than the diameter of each of the liquid feed pipe lines to be connected to an upstream side and to a downstream side thereof. The container for the deaerating unit covers not only the outer peripheral surface of the hollow fiber membrane but also an upstream side end surface and a downstream side end surface thereof. Accordingly, the entire periphery (entire length) of the hollow fiber membrane is completely covered with the container.
Further, the inkjet head of this type has a liquid material ejection port opened therein for ejecting an ink or a film material onto one end surface, and the ink is ejected and supplied to a print medium such as paper from the liquid material ejection port, or a liquid film material is ejected and supplied to a transparent substrate of a display device or the like.
In the inkjet head of this type, the ink or the film material is ejected from the liquid material ejection port having an extremely small opening area. As a result, the liquid material itself or a pigment, for example, contained in the liquid material is solidified, for example, and attaches to the liquid material ejection port and the vicinity thereof. In addition, foreign matters such as dust contained in the outside air are also attached to the liquid material ejection port and the vicinity thereof. This causes an ejection failure of the liquid material, and inhibits the printing on the print medium and formation of the oriented film.
Therefore, in the inkjet head of this type, for the purpose of recovering a liquid material ejection function of the inkjet head to an excellent state at appropriate time intervals before causing those problems, the cleaning mobile unit for cleaning the liquid material ejection port and/or the vicinity thereof is provided. As the cleaning mobile unit, there is known one including negative pressure suction means for sucking and removing a solidified material and foreign matters attached the liquid material ejection port and/or the vicinity thereof, by a suction force due to a negative pressure.
As an example of the cleaning mobile unit, Patent Document 6 described below discloses a technology for directly bringing a vacuum hood of the cleaning mobile unit into contact with the one end surface in which material ejection ports of the inkjet head (print head) are opened, to perform negative pressure suction through the vacuum hood with respect to not only the material ejection port but also the inside thereof. Patent Documents 7 and 8 described below disclose a structure in which a vacuum nozzle is provided to the cleaning mobile unit, and the vacuum nozzle itself is not brought into contact with the one end surface in which the material ejection ports of the inkjet head are opened.
[Patent Document 1] JP 2002-307708 A
[Patent Document 2] JP 2003-88778 A
[Patent Document 3] JP 5-17712 A
[Patent Document 4] JP 10-298470 A
[Patent Document 5] JP 11-209670 A
[Patent Document 6] JP 2000-190514 A
[Patent Document 7] JP 6-126972 A
[Patent Document 8] JP 8-118668 A